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a combining form occurring in loanwords from Greek and Latin, where it meant “eight” (octagon; octastyle), on this model, used in the formation of compound words, and in chemical terms specialized to mean “having eight atoms” (octavalent).
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Also oct-, octo-.

Origin of octa-

<Greek okta-, combining form of oktṓeight
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2023


What does octa- mean?

Octa- is a combining form used like a prefix meaning “eight.” It is often used in a great many scientific and technical terms.

Octa- comes from Greek oktṓ, meaning “eight.” The Latin equivalent, which is almost identical in spelling and pronunciation, is octō.

What are variants of octa-?

When combined with words or word elements that begin with a vowel, octa- becomes oct-, as in octane. Another variant of octa- is octo-, as in octofoil.

Want to know more? Check out our Words That Use entries for both oct– and octo-.

Examples of octa-

An example of a word you may have encountered that features octa- is octagon, “a polygon having eight angles and eight sides.” Octagon comes from Greek oktágōnos, which features the equivalent of the form octa-.

We know octa- means “eight,” but what about the -gon portion of the word? The form -gon, from Greek gōnía, means “angled, angular.” Octagon literally translates to “eight-angled.”

What are some words that use the combining form octa-?

What are some other forms that octa- may be commonly confused with?

Break it down!

The combining form -hedron means “face” and is used in the names of geometric figures with a certain number of faces. With this in mind, what is an octahedron?

How to use octa- in a sentence

  • After this Eosa and the rest that fled, being encouraged by Octa's success, came also, and were admitted to the same favour.

  • The incautious sovereign having assented to this, Octa and Ebusa arrived with forty ships.

British Dictionary definitions for octa- (1 of 2)

/ (ˈɒktə) /

a variant spelling of okta

British Dictionary definitions for octa- (2 of 2)


combining form
a variant of octo-
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012